Hello, this came up because these rom files are somewhat difficult to build on non-x86, and distributions that have problem with distributing blobs verbatim may be missing them.
On Tue, Feb 18, 2025 at 01:38:42PM +0300, Michael Tokarev wrote: > Hi! > > Qemu system-mode emulation, when used with a NIC, loads a ROM file > for network booting (and fails to start if such file is not provided). > ROMs shipped in the source tarball are x86-only, so such loading does > nothing on non-x86, where we just wasting guest memory, - since the > ROM code can not be executed on the target architecture anyway. > > These days, ipxe provides (UEFI) ROM files for architectures other than > x86. And these ROMs actually works, making it possible to network-boot > qemu guests in UEFI mode. > > Would it be possible to make ROMs target-arch-specific, and drop the > ROM dependency/loading on non-x86 if there's no arch-specific ROM found? > This probably requires machine version dependency, to make the machine > migratable. Currently, romfile is a static property of a device, > independent of the architecture. And for emulation of a specific device (eg. e1000) it makes sense that it comes with a ROM, even if the architecture does not make use of it. That's how the hardware looks. And while it may be unusual the ROM can be empty, eg. because somebody used a tool to erase it. That is using an empty ROM as a fallback is something that is reasonable emulation of the hardware in question, or no ROM at all for devices like virtio. > A similar question exists about seabios and vgabios - for example, > virtio-vga device always tries to load vgabios.rom on all architectures, > while on non-x86 it is useless. In this case it is more dodgy. I vaguely recall some code for interpreting these BIOSes somewhere. That is the x86 BIOS can run in some emulation to provide the BIOS functionality on non-x86. Not sure how much it's actually used in practice for the kinds of cards that qemu emulates. Thanks Michal
